Internal or closed batch mixers have been commercially available for many years for mixing polymeric materials, such as plastics and rubber materials. The quality of the plastic or rubber products produced in the mixer can be influenced by mixing process parameters that are variable, such as fluctuations in the mixer temperature, the cooling water temperature, the material feed temperature, the ram pressure, the rotor speed, the time of mixing, the fill level, the speed of the fill, and the like.
During the processing of these polymeric materials, many times various ingredients, such as oil, fillers, curatives, antioxidants, etc., hereinafter additives, are added to the polymeric materials while in the mixer. These additives can be combined with the polymeric materials for a variety of reasons. For example, the additives may improve the stability of the polymeric material during processing. Alternatively, the additives may improve the performance characteristics of the polymeric material after processing is complete by providing, for example, increased resistance to UV degradation or improved wearing characteristics. However, some of these additives can only be added to the polymeric material in the mixer when the polymeric material is at a certain temperature. If the temperature of the polymeric material is too high, the effectiveness of the additive is impaired.
Thus, the polymeric material would have to be discharged from the mixer to allow the mixture to cool. Then, after cooling, the polymeric mixture was reintroduced into the mixer so that the various additives could be added to the polymeric mixture. As can be understood, this greatly increased the process time and cost for processing these compounds.